Soru Jewellery, a UK-based brand, writes on Facebook that the pair is theirs. They link to a page describing the earrings as "18ct Yellow gold vermeil on sterling silver earrings for pierced ears. Hand crafted with iridescent baroque pearls set within multi faceted Swarovski crystals." (I think the earrings look like a slightly different shape than the one linked by the brand, but the materials look to be the same.) The earrings were reportedly purchased at one of the company's stockists, Baar and Bass.

UPDATE: Soru Jewellery has stated that the earrings are not yet available online, but they have updated their site with a page showing the precise earrings Kate wore. They'll reportedly be available at this link in the near future. The earrings retail for £130.